The present invention relates to metal gaskets to be used for sealing means and more particularly to a method of making metal gaskets to be used as sealing means for large diameter vacuum gate valves to be used for nuclear fusion apparatus and the like, gate valves for high temperatures, gate valves for low temperatures, flanges and the like.
A conventional example used for flanges among metal gaskets for sealing means so far applied to the above mentioned uses shall be described. In FIG. 1, the mating faces of upper and lower flanges h and i, fitted respectively to the ends of pipings f and g, are provided with respective grooves m and n for confining a metal gasket a to seal the flange parts. As shown in FIGS. 2 and 3, metal gasket a is shaped in the form of a truncated conical tubular member. Symbols b and c indicate contact surfaces (end surfaces of sealing ends) parallel with the center axis of said metal gasket a, symbol d indicates its inner surface and e indicates its outer surface. This metal gasket a is made by cutting a resilient spring steel to form a truncated conical tubular member as mentioned above, and plating or coating it on the above mentioned respective surfaces b to e.
In this kind of metal gasket, the sharp edge parts (sealing ends) b.sub.1 and c.sub.1 at the upper and lower ends are the life. In the method wherein, as mentioned above, a spring steel is cut off to form a truncated conical tubular member which is then plated, it is difficult to uniformly plate sharp edge b.sub.1 and c.sub.1 and to form said parts plating uniformly over the entire periphery. Since the precision of the inside and outside diameters of the metal gasket can not be increased the durability as of these known gaskets has been low.
Further, in order to improve the sealing effect, it is necessary to increase the thickness of the plating layer. However, in the method wherein, as mentioned above, the gasket is cut off to be truncated conical tubular and is then plated, the respective inner and outer surfaces d and e, which actually do not require a plating layer, will be also plated. Thus, the prior technique has not been an economical method.